BMI Calculator
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BMI (Body Mass Index) is a single number that estimates body fat from your height and weight. It's the standard adult health screening metric used by the CDC and WHO. Enter your height and weight — the calculator gives you the number; the sections below explain how to interpret it and where it breaks down.
The four standard categories for adults: under 18.5 is underweight, 18.5–24.9 is normal weight, 25.0–29.9 is overweight, and 30.0 and above is obese. These bands are population-level guidelines, not individual diagnoses.
Key takeaway
BMI is a population-scale screening tool, not a body-composition measurement. It treats weight as a proxy for body fat — which works on average but breaks down for muscular individuals, very tall or very short people, the elderly, and across different ethnic groups. A muscular athlete and a sedentary person can share an identical BMI while being in completely different health states. Treat the number as one input, not a verdict.
How it's calculated
The imperial formula is BMI = (weight in pounds × 703) / (height in inches)².
The metric form is the cleaner one: BMI = weight in kg / (height in meters)² —
no magic constant. The 703 factor exists only to convert pounds-and-inches into
metric-equivalent units. Both formulas produce the same number for the same person.
Source: CDC adult BMI categories
Quick tricks
- Underweight: under 18.5 Categorizing low BMI — often warrants a conversation with a doctor about underlying causes.
- Normal: 18.5 to 24.9 The CDC/WHO 'healthy weight' band for the general adult population.
- Overweight: 25 to 29.9 Increased risk for cardiovascular and metabolic conditions, but not a diagnosis on its own.
- Obese: 30 and above BMI 30+ correlates with significant health risks at the population level. Class I (30–34.9), II (35–39.9), III (40+).
- BMI underestimates body fat in older adults and overestimates it in athletes. Interpreting your own number. Body fat % from a DEXA scan is the gold standard if BMI seems off.
Examples
5'9" tall, 165 lb
At 5'9" (69 inches) and 165 lb, BMI works out to 24.4 — within the normal range but near the upper boundary. Gaining 8 lb would push it past 25 into the overweight band.
6'2" tall, 210 lb
At 6'2" (74 inches) and 210 lb, BMI is 27.0 — overweight by the standard bands. For a person carrying significant muscle mass at this height, the BMI category may overstate health risk; body fat percentage gives a clearer picture in that case.
Frequently asked questions
Is BMI accurate for everyone?
No. BMI works as a population-level screening tool but breaks down for individuals at the extremes — very muscular people (athletes, weightlifters), the elderly (who lose muscle mass), pregnant women, and across different ethnic groups (the WHO has noted Asian populations face elevated risk at lower BMIs than the standard cutoffs suggest). For an individual reading, body fat percentage from a DEXA or BodPod scan is more accurate.
What's the difference between BMI and body fat percentage?
BMI is a ratio of weight to height-squared — it doesn't know how much of your weight is muscle, fat, bone, or water. Body fat percentage measures how much of your total mass is fat tissue specifically. A 200 lb athlete with 10% body fat and a 200 lb sedentary person with 30% body fat have the same BMI but very different metabolic profiles.
Should I be worried about a BMI in the "overweight" range?
Not necessarily. The 25–29.9 range is associated with elevated population-level risk for some conditions, but individual risk depends on body composition, muscle mass, fitness level, blood pressure, lipid profile, and family history. A BMI of 27 with low body fat, normal blood work, and regular exercise is very different from a BMI of 27 with high visceral fat and metabolic syndrome.
Is BMI the same for men and women?
The cutoffs are the same, yes. But the relationship between BMI and body fat differs — women on average have higher body fat percentages than men at the same BMI. This is one reason why some clinicians supplement BMI with waist circumference (under 35" for women, under 40" for men is the standard threshold) for a fuller picture.